The effect and value of silver iodide in a silver halide grain is well known to the art. For example, Duffin, "Photographic Emulsion Chemistry," The Focal Press, 1966, page 64, refers to the effect of iodide on the rapidity of grain growth as well as the increased photographic speed and improved spectral sensitization.
Mees, "The Theory of the Photographic Process," McMillan Co., 1946, page 316, reports the treatment of silver bromide grains with potassium iodide to convert the surface of the grain at least partially to silver iodide for the purpose of modulating the rate of reduction of the grain.
Similar disclosures are also found in a number of patents as illustrated by the following:
U.S. Pat. No. 3,561,971 discloses a silver halide emulsion, generally of the print-out type, wherein the grains comprise silver bromide having from 0.2 to 10 mole percent silver iodide on the surface thereof.
Other patents such as U.S. Pat. Nos. 3,477,852 and 3,597,209 disclose "converted" type emulsions where the halide on the surface is replaced by a different halide, such as the "conversion" of chloride to bromide.